JP2001328807A - Method of purifying quartz powder and product made of quartz powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a purification process and an apparatus therefor which can efficiently remove the metal impurities from quartz powder with simple constitution. SOLUTION: A purification vessel that is equipped with a partition wall made of quartz glass between the anode and the cathode is used to form an electric field in the quartz powder charged on both sides of the partition wall under high temperature whereby the metal impurities are allowed to move toward the anode side and the metal impurities is lowered in the quartz powder on the cathode side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a purification method and apparatus for reducing the amount of impurity metals such as alkali metals, iron, and copper contained in quartz powder and products using the purified quartz powder. More specifically, quartz glass materials for the semiconductor industry,
The present invention relates to a technique for purifying natural quartz powder and the like used as a raw material for a quartz crucible for pulling up silicon.

[0002]

2. Description of the Related Art Natural quartz contains a trace amount of alkali metal. When the quartz powder containing the alkali metal is used for a heat treatment member for the semiconductor industry such as a quartz glass crucible or the like, the member is deformed or devitrified. In the case of a quartz glass crucible used for pulling a silicon single crystal, there is a problem that the silicon single crystal is contaminated by an alkali metal contained in the crucible. Therefore, in order to remove alkali metal impurities from natural quartz or the like, (a) a method of applying an electric field to concentrate the alkali metal on the cathode side, or (b) introducing a chlorine-containing gas at a high temperature, etc. A purification method such as a method of converting a metal into a chloride to volatilize and remove the metal has been conventionally known.

For example, JP-A-59-129421 and JP-A-6-129421
JP-A-137892 and JP-A-06-16494 disclose a quartz ingot or a quartz glass crucible product of 1200
It is described that an alkali metal ion or a copper ion in a product is moved by applying a direct current of 10 to 50 kv while heating at a temperature of １1300 ° C. However, these electrolytic refining methods relate to glass products, and it is difficult to apply them directly to quartz powder. In the case of glass products, an alkali metal can be concentrated on a part of the product by attaching electrodes to the product surface and energizing it.However, particles of the quartz powder are fluidized. Even if the metal is concentrated on the cathode side, a sufficient refining effect cannot be obtained if the quartz powder on the cathode side and the quartz powder on the anode side are mixed when the quartz powder is taken out after energization.

[0004] On the other hand, a method of purifying quartz powder using a chlorine-containing gas or the like has been conventionally known. For example,
55-42267, JP-A-62-30632, JP-A-63-100
No. 038 describes that a natural quartz powder or the like is subjected to a heat treatment in a chlorine-containing gas stream to convert an alkali metal or the like into a chloride and volatilize and separate the chloride. These conventional refining methods can provide some effect for sodium and potassium contained in quartz powder, but have a problem that sufficient refining effect cannot be obtained for lithium. Further, when chlorine gas is used, there is a disadvantage that the exhaust gas treatment is troublesome.

Further, US Pat. No. 4,956,069 discloses that
An apparatus for introducing a chlorine-containing gas into a horizontal rotary furnace charged with quartz powder and purifying the quartz powder through an electric current is described. In this refining apparatus, a horizontal kiln is used in order to stabilize the configuration of the apparatus, and the kiln is rotated to disperse and flow the quartz powder to contact the chlorine-containing gas. This mechanical rotation mechanism tends to increase the size of the device,
In addition, the structure of the electrodes and the gas flow is limited around the rotating shaft so as not to hinder the rotation, so that the device configuration becomes complicated. In addition, since the contact between the quartz powder and the gas is not always good, the refining effect is not good. Further, in this refining apparatus, since the quartz powder is rotated, there is a problem that the electrode material is shaved by the quartz powder, and this is mixed with the quartz powder to become an impurity. In particular, if the electrode material is made of silicon carbide (SiC), the silicon carbide mixed in the quartz powder generates bubbles when the quartz is melted, resulting in crucible defects. In addition, this equipment introduces chlorine-containing gas into the furnace to convert alkali metals into chlorides, which are volatilized and removed. There is a possibility that the substance condenses and mixes with the quartz powder to become an impurity.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the conventional refining technology. The present invention solves the problem of removing impurities such as alkali metals, copper, and iron contained in quartz powder with a simple structure and at a high efficiency. It is intended to provide a purification technique that can be reduced well.

[0007]

That is, the present invention provides:
(1) Using a purification vessel provided with a quartz glass partition wall between the anode and the cathode, forming an electric field at high temperature on the quartz powder charged on both sides of the partition wall at a high temperature, and forming an impurity metal contained in the quartz powder. To a method for purifying quartz powder, characterized in that the amount of impurity metal in the quartz powder on the anode side is reduced by moving the powder to the cathode side.

[0008] The purification method of the present invention preferably comprises
(2) a method of electrolytically refining quartz powder in a nitrogen gas atmosphere, an air atmosphere, or an atmosphere containing a small amount of hydrogen or water therein;
A purification method for performing electrolytic refining of quartz powder by forming an electric field of 50 V / cm or more at a high temperature of 00 to 1300 ° C. (4) The content of lithium, potassium, sodium, copper, and iron is 0.1 ppm or less in each case. Purification method to reduce to (5)
A quartz glass container having a double-tube structure having an inner tube inside the outer tube, using a purification container provided with electrodes on the peripheral surface of the outer tube and inside the inner tube, and each of the outer and inner tubes being made of quartz. A method of charging and purifying the powder, (6) having electrodes on both sides of a rectangular container,
The method includes a purification method using a purification container made of quartz glass whose inside is partitioned by partition walls.

Further, the present invention provides (7) a purifying vessel containing quartz powder and a heating means, wherein the purifying vessel is a quartz glass vessel having a double tube structure having an outer cylinder and an inner cylinder inside thereof. An apparatus for purifying quartz powder, comprising: electrodes on the outer surface of the outer tube and the inner surface of the inner tube, and further provided with an air passage communicating with the inside of the container. And a heating means, electrodes are provided on both sides of the container, the inside is partitioned by partition walls, and an air passage leading to the inside of the container is further provided.

[0010] The present invention further relates to (9) a quartz glass product produced from the quartz powder refined by any of the above (1) to (6).

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments. FIG. 1 is a schematic cross-sectional view of a vertical cylindrical device according to the present invention, FIG. 2 is a schematic transverse cross-sectional view thereof, and FIGS.

(I) Purification Method As shown in the figure, the purification method of the present invention uses an electrolytic purification vessel provided with an anode and a cathode and having a partition wall between both electrodes. The partition walls are preferably made of quartz glass so that the movement of impurity metal ions such as alkali metals released from the quartz powder is not hindered. The shape of the purification vessel is not limited as long as it has an anode, a cathode, and a partition. It may be cylindrical or square. Figures 1 and 2 show examples of purification vessels.
Can be used. The container 10 has a double-pipe structure including an outer cylinder 11 and an inner cylinder 12, the inner cylinder 12 serving as a partition wall, and a strip-shaped anode or cathode 13 surrounding the lower inner periphery of the outer cylinder 11. A pair of rod-shaped electrodes 14 is provided on the axis of the inner cylinder 12.

Another example of a purification vessel is shown in FIG.
An anode 33 or a cathode 34 is provided at an upper end and a lower end of a vertical cylindrical container 31, and a partition 32 that vertically partitions the inside of the container.
May be provided. Further, as shown in FIG. 4, an anode 41 or a cathode 42 may be provided on both sides of a rectangular container 40, and a partition 43 may be provided therebetween. The material of the anode and the cathode is preferably carbon or platinum. When a quartz glass container is used as the electrode of the outer cylinder or the electrode of the rectangular container, the electrode may be closely attached to the outer periphery of the container. By mounting the electrode on the outer periphery of the container, it is possible to prevent the electrode from being worn by the flow of the quartz powder. Even if electrodes are provided on the outer periphery of the quartz glass container, a sufficient electric field can be applied to the quartz powder if the electrodes are provided in close contact. It is preferable that at least one of the electrodes is formed in a planar shape so that an electric field is uniformly applied to the entire quartz powder.

A quartz powder is filled between the anode and the cathode so as to be in close contact with the partition wall of the electrolytic vessel, and a high-voltage electric field is applied to the quartz powder at a high temperature by applying a DC voltage through the electrodes. Specifically, at a high temperature of 800 to 1300 ° C., 50
An electric field of at least V / cm, preferably at least 100 V / cm, more preferably at least 500 V / cm is applied. The energization time may be adjusted according to the amount of the quartz powder. When a carbon electrode is used, it is preferable that the container is closed and the inside is a nitrogen gas atmosphere in order to prevent deterioration of the electrode due to oxidation. Argon gas is not preferable because it easily causes discharge. In the case of a platinum electrode or the like, the atmosphere may be an air atmosphere, and the interior of the container need not be sealed.

The purification effect can be enhanced by adding a small amount of hydrogen or water to the nitrogen gas atmosphere or air atmosphere. The amount of addition is the concentration in the atmosphere, 1-5 wt% for hydrogen, 5-5 for water (steam).
30 wt% is preferred.

When an electric field is applied to the quartz powder in the container, impurity metals such as alkali metals contained in the quartz powder are ionized and attracted to the cathode. Since the partition is made of quartz glass like the quartz powder, impurity metal ions contained in the quartz powder on the anode side move to the cathode side through the partition.
As a result, the amount of impurity metal contained in the quartz particles on the anode side is reduced, and the quartz powder can be purified. Impurity metal ions such as alkali metals concentrate in the quartz particles on the cathode side, but since the anode side and the cathode side are separated by partition walls, both quartz powders are not mixed, and the purified quartz on the anode side The powder can be separated and recovered from the quartz powder on the cathode side. The quartz powder on the cathode side can be reused.

As described above, according to the above-mentioned purification method of the present invention, by applying an electric field to quartz powder through a quartz glass partition, impurity metal ions such as alkali metals move to the cathode side through the partition. In addition, the amount of impurity metal in the anode-side quartz powder is reduced, an excellent refining effect can be obtained, and the purified quartz powder on the anode side and the quartz powder on the cathode side can be separated and collected by the partition walls.

The conventional purification method using chlorine gas or the like has a particularly low purification effect on lithium. However, according to the purification method of the present invention, since the alkali metal is ionized by the action of an electric field, the purification effect on lithium is also good. Can be obtained. Specifically, any of lithium, potassium and sodium is 0.1 ppm or less, preferably 0.05 ppm.
It can be reduced below. Therefore, by using the quartz powder purified by the method of the present invention, a quartz glass product having significantly less alkali metal impurities can be obtained.

(II) Refining Apparatus The refining apparatus shown in FIGS. 1 and 2 according to the present invention comprises, as shown in FIG.
(Not shown). The container 10 is formed by a vertical outer cylinder 11 and a quartz glass inner cylinder 12 provided at a constant interval inside the outer cylinder 11, and has a double tube structure composed of the outer cylinder 11 and the inner cylinder 12. Have. The outer cylinder 11 and the inner cylinder 12 can be made of quartz glass. An electric field can be effectively applied to the entire quartz powder by using an outer cylinder and an inner cylinder made of quartz glass and providing electrodes on the outer peripheral wall and inside of the inner cylinder. Specifically, an anode 13 made of carbon is provided on the peripheral surface of the outer cylinder 11 around the inner periphery of the outer cylinder, while a rod-shaped cathode 14 is provided at the center of the inner cylinder 12. . Lids 15, 16 are crowned on the heads of the outer cylinder 11 and the inner cylinder 12, respectively.
The inner cylinder 12 is supported by the lid 15 of the outer cylinder 11 so as not to fall down. The insides of the outer cylinder 11 and the inner cylinder 12 are sealed by lids 15 and 16. These lids 15, 16
Have openings 21 and 2 for supplying quartz powder inside
2 are provided. Further, the bottom of the outer cylinder 11 is formed of a permeable flooring material 17, and the ventilation chamber 1
8 are formed. A ventilation path 20 is connected to the ventilation chamber 18, and an exhaust pipe 19 is connected to the lid 15 corresponding to the ventilation path 20. The ventilation path 20 may be directly connected to the bottom of the outer cylinder without providing the ventilation chamber 18.

A quartz powder is filled into the outer cylinder 11 and the inner cylinder 12 at the height of the anode 13, and a nitrogen gas is introduced into the vessel filled with the quartz powder to protect the carbon electrode. The inside of the vessel is heated to 800 to 1300 ° C. by a heater (not shown)
An electric field of 50 V / cm or more, preferably 500 V / cm or more is applied to the quartz powder through 3, 14. When a platinum electrode is used, it is not necessary to introduce nitrogen gas into the container.

Due to the action of the electric field, impurity metals such as alkali metals contained in the quartz powder filled between the outer cylinder 11 and the inner cylinder 12 are ionized, move through the inner cylinder 12 to the cathode side, and move to the cathode side. It concentrates inside the cylinder 12. As a result, the amount of impurity metal in the quartz particles on the outer cylinder side is reduced. After purification, lid 15
And take out the purified quartz powder 50 on the outer cylinder side. On the other hand, the quartz powder 50 in the inner cylinder 12 may be filled with new quartz powder in the outer cylinder while continuing to fill the inner cylinder, and electrolytic refining may be continued. It may be mixed with quartz powder and reused.

The apparatus configuration shown in FIG. 3 is such that the inside of a vertical container 31 is vertically divided by a partition wall 32, and a cylindrical container 3 is provided.
An anode 34 and a discharge port 35 are provided at the bottom of the container 1, while a lid 37 is mounted on the head of the container 31, and a cathode 33 is provided on the lid 37. The partition 32 is made of quartz glass and is loosely fitted inside the container. Note that a cathode may be provided at the bottom of the container and an anode may be provided at the head.

After the lid 37 of the container 31 is opened and the quartz powder is charged into the vicinity of the head, the partition wall 32 is placed on the quartz powder, the quartz powder is put thereon, and the lid 37 is closed.
Next, a voltage is applied through the electrodes 33 and 34 to apply an electric field to the quartz powder. The action of this electric field reduces the amount of alkali metal in the quartz powder on the anode side. After stopping the power supply, the discharge port 35 is opened to take out the quartz powder inside the container. As the purified quartz powder 50 on the anode side is extracted from the outlet 35, the partition wall 32 gradually descends by its own weight, and closes the outlet 35 when the discharge of the purified quartz powder is completed. Remains inside.

The apparatus shown in FIG. 4 uses a rectangular container 40. An anode 41 and a cathode 42 are provided on both sides of the container 40.
Is interposed. The upper surface of the container 40 is closed by a lid 44. The inside of the container is filled with quartz powder 50 so as to be in contact with the anode 41, the cathode 42 and the partition 43. By applying an electric field to the quartz powder 50, the amount of impurity metals in the quartz powder on the anode side can be reduced.

(III) Purification Example Using a purification apparatus having the apparatus configuration shown in FIGS. 1 and 2, 20 kg of quartz powder was charged into a vessel (outer cylinder and inner cylinder), and nitrogen was placed inside the vessel to protect the carbon electrode. 1 after introducing gas
The mixture was heated to 200 ° C., and a DC voltage of 15 kv was applied to the quartz powder for 6 hours. After this electrolytic purification, the concentrations of lithium, sodium, and potassium contained in the quartz powder were quantified. The results are shown in Table 1 No. 1. Compared with the quartz powder before the treatment, the alkali metal concentration of the quartz powder (20 kg) on the outer cylinder side is greatly reduced, and especially lithium is 0.01 ppm, which is about 1/2.
It has dropped sharply to zero. In addition, the concentrations of sodium and potassium were 0.1 ppm or less, and an excellent purification effect was obtained. On the other hand, the amount of alkali metal in the quartz powder (20 kg) on the inner cylinder side is increasing, and it can be seen that the alkali metal contained in the quartz powder on the outer cylinder moved to and concentrated on the quartz powder on the inner cylinder side.

The voltage application time was changed to 3 hours, and the atmosphere in the container was a nitrogen gas atmosphere (No. 2), a nitrogen gas atmosphere (No. 3) mixed with 2 wt% of hydrogen, and a nitrogen gas atmosphere mixed with 15 wt% of steam. (No. 4), except that the quartz powder was electrolytically purified in the same manner as above. The results are shown in Table 1. As shown in the results, it was confirmed that the refining effect was significantly improved by mixing a small amount of hydrogen or steam into the nitrogen gas. That is, the purification time of Nos. 3 to 4 was N
o. 1/2 of alkali metal, copper and iron
o.1 Achieved a greater removal effect than the case of 1.

[0027]

[Table 1]

[0028]

According to the refining method and the refining apparatus of the present invention, impurity metals such as alkali metal, copper, and iron contained in quartz powder can be reduced efficiently with a simple structure.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a cylindrical device according to the present invention.

FIG. 2 is a schematic cross-sectional view of the apparatus shown in FIG.

FIG. 3 is a schematic longitudinal sectional view showing another example of the device configuration according to the present invention.

FIG. 4 is a schematic longitudinal sectional view showing another example of the device configuration according to the present invention.

[Explanation of symbols]

10-refiner, 11-outer cylinder, 12-inner cylinder, 13-anode, 14-cathode, 15,16-lid, 17-floor, 18-vent room, 19-exhaust line, 20-vent line, 21, 22-opening, 31-container, 32-partition, 33-cathode, 34-anode, 35-discharge, 37-lid, 40-container, 41-anode, 42-cathode, 43-partition, 44- lid

Claims (9)

[Claims] 1. A purification vessel having a quartz glass partition wall between an anode and a cathode is used. An electric field is formed at a high temperature on the quartz powder charged on both sides of the partition wall, and the quartz powder is contained in the quartz powder. A method for purifying quartz powder, comprising reducing the amount of impurity metal in the quartz powder on the anode side by moving the impurity metal to the cathode side. 2. The method according to claim 1, wherein the quartz powder is electrorefined in a nitrogen gas atmosphere, an air atmosphere, or an atmosphere containing a small amount of hydrogen or water. 3. The method according to claim 1, wherein the quartz powder in the refining vessel contains 800 to 13 particles.
The method according to claim 1 or 2, wherein the quartz powder is subjected to electrolytic refining by forming an electric field of 50 V / cm or more at a high temperature of 00 ° C. 4. Lithium, potassium, sodium, copper,
4. The method according to claim 1, wherein the iron content is reduced to 0.1 ppm or less. 5. A quartz glass container having a double tube structure having an inner cylinder inside an outer cylinder, wherein a purification vessel having a peripheral surface of the outer cylinder and electrodes provided inside the inner cylinder is used. 2. The refining method according to claim 1, wherein quartz powder is charged into the inner cylinder for purification. 6. The refining method according to claim 1, wherein an electrode is provided on both sides of the rectangular container, and a refining container made of quartz glass is used. 7. A refining vessel for holding quartz powder and a heating means, wherein the refining vessel is a quartz glass vessel having a double tube structure having an outer cylinder and an inner cylinder inside thereof, wherein the outer peripheral cylinder has a peripheral surface. An apparatus for purifying quartz powder, comprising: an electrode inside an inner cylinder; and a ventilation path communicating with the inside of the container. 8. A prismatic quartz glass refining container and a heating means are provided, electrodes are provided on both sides of the container, the inside is partitioned by partition walls, and an air passage leading to the inside of the container is provided. An apparatus for refining quartz powder. 9. A quartz glass product produced from quartz powder refined by the method according to claim 1.